The present invention is directed to a bipolar cutter/coagulator for use in surgery. The cutter/coagulator may be employed to cut and repair tissues and is particularly required for use in microsurgery.
Prior art monopolar and bipolar coagulators used spark-gap generators to produce an aperiodic sequence of radio frequency (RF) bursts having random spike components. Such waveforms produce the best coagulation. However, the initial spike of each damped burst is much higher in voltage than the rest of the burst, as a requirement for striking the arc in the spark-gap. This high initial voltage spike is responsible for undesirable sparking at the forceps tips and produces television and monitoring equipment interference.
Electronic tube or solid state coagulators generally provide regularly occurring bursts of damped sine waves, square waves, or undamped pulses as the coagulating waveform. The regular occurrence of these waveforms increases undesirable cutting or perforation of vessels during coagulation, as a result of induced molecular resonance.
The present invention simulates the aperiodic RF bursts of the spark gap systems, but the leading voltage spike in each burst is controlled, the burst envelopes are uniform from burst to burst, and the intra-burst RF frequency is randomized. The new waveform results in the elimination of molecular resonance, hence undesirable cutting or perforation during coagulation. Control of the first spike of each burst also results in marked reduction of sparking of the forceps as well as reduction of interference with other equipment in the operating room. The waveform parameters namely, inter-burst spacing, intraburst RF frequency, and the spacing between consecutive sequence of bursts, produce the smoothest coagulation, least neuromuscular stimulation, the least pitting of the forceps as well as the least charring and sticking at the forceps, and the least vascular perforation.
Monopolar coagulators have long been used in surgery. Monopolar coagulators provide a current path from a single active electrode through the patient to a return or ground plate. The highest power per tissue volume is produced at the active electrode. The most conductive path to ground receives the highest current density, so that appreciable current can be distributed in adjacent tissues. The most conductive path can be through the blood. In a small vessel being coagulated, current can flow through the blood and coagulate the parent vessel inadvertently. Moreover, use of the monopolar coagulator under saline irrigation is not feasible, since the saline rather than the desired tissue can furnish the most conductive path to ground.
Bipolar coagulator, as compared with monopolar, utilize a pair of forcep electrodes coupled by cable to isolated power outputs. The forcep blades are insulated from each other. The power output of the bipolar coagulator is isolated from ground, so that current flow is restricted to a zone between the forcep tips. Current does not flow from either forcep tip to ground. The current path geometry depends primarily on the tip size, the angle at which the tips meet, and the conductivity of the medium in which the tips are immersed. If the forceps blades are virtually parallel and are deeply immersed in saline, there can be major shunting of current through the saline despite isolation of the power output. But if the forceps blades are bowed or angled so that the tips almost meet while the parallel portion of the blades remain well-separated, current flow is restricted to the zone between the tips with little shunting through the saline.
The power output section of a bipolar cutter/coagulator should have a low output impedance to maintain uniform power at the forcep tips over a wide range of load conditions, from dry tissue to heavily irrigated tissue. The present invention provides a stiffly regulated, isolated power output with an output impedance of approximately 5-10 ohms. By contrast, the output impedances of previously available solid state systems are approximately 50-500 ohms, and even the best spark gap coagulator has an output impedance of 40-50 ohms. The lower output impedance of the present invention facilitates its use under the constant irrigation desirable for cooling and protecting adjacent delicate vessel, tissue and nerve structures.